The present invention relates to an exhaust cooling system of an amphibious vehicle.
In the case of dedicated land vehicles and marine vessels known in the art, the apparatus and methods employed for cooling exhaust systems are well established. In the case of a land vehicle, the exhaust system is typically slung below the floor panel of the vehicle such that it is exposed to ambient atmospheric air which passes over and cools external surfaces of the exhaust system. The cooling effect achieved is of course variable but satisfactory, being largely dependent upon factors such as vehicle speed and atmospheric conditions. In the case of marine vessels, it is usual to cool exhaust systems with water. This is normally achieved using the abundant resource of raw water outside the vessel which is drawn in and circulated around a water jacket enclosing the exhaust system and then exhausted back to the raw water source. Such exhaust cooling systems are highly efficient when the marine vessel is on water, but do not function when on land where the raw water source is no longer available. However, this is not particularly important for a marine vessel whose engine will only rarely be run on land, if at all (typically only for maintenance reasons where an artificial raw water source may be provided, e.g. via a hosepipe).
It is also known from U.S. Pat. No. 3,884,194 of Citroen to provide a water jacket for an exhaust manifold of an air cooled engine used in a land vehicle in order to recover heat energy. In particular, U.S. Pat. No. 3,884,194 discloses a steam generator used for heating the passenger compartment of vehicles equipped with air cooled engines.
In U.S. Pat. No. 4,991,546 of Sanshin Kogyo Kabushiki Kaisha, there is disclosed a water jacket based cooling system for marine watercraft used to cool both the internal combustion engine and exhaust manifold. The invention is concerned with preventing condensation forming in the exhaust manifold as a result of the cooling process. Raw water is used, this being sourced from outside the watercraft and is returned after circulation around the various water jackets of the system. In one embodiment, a supplementary radiator is used, but only for the purpose of providing a sealed cooling jacket for the engine, exhaust manifold and a portion of an exhaust elbow so that a coolant other than pure water may be employed in a closed system and kept separate from the raw water. Raw water is still required to be sourced, circulated and returned to the body of water outside of the watercraft. As such, this system cannot be employed in a land vehicle.
In the case of an amphibious vehicle, however, the problems of cooling of an exhaust system present quite unique problems and considerations. An amphibious vehicle is used extensively on land and on water and its exhaust system is liable to run at least as hot as that of any other road vehicle. Whereas land vehicles rely on the surrounding air to keep their exhaust systems cool, especially catalytic converters which have been known to run so hot (˜900° C.) as to ignite grass underneath parked vehicles, the underside of an amphibious vehicle is sealed to ensure buoyancy and hydrodynamic performance on water. This compounds the problem of providing adequate cooling since sealing the exhaust system inside the hull actually serves to insulate it from external cooling influences. Furthermore, it is desirable to seal in the exhaust system of an amphibious vehicle since there exists the potential for damaging thermal shock effects of quenching when a fully heated exhaust system which has been operating in land mode enters the water for the vehicle to operate in marine mode. Also, the catalytic converter is a very sensitive item which must be maintained at its optimum operating temperature to prevent damage to the catalyst. It is clear therefore that an amphibious vehicle presents conflicting requirements and dedicated prior art systems are poorly suited to the requirements of an amphibious vehicle.